Spray elastomer systems are commonly recognized as coating mate-rials, with aliphatic and aromatic isocyanate spray polyurea elastomer systems being particularly useful when employed in this capacity. This two-component technology is based on an isocyanate quasi-prepolymer and an amine coreactant, often an amine resin blend.
It is further known to use spray polyurea elastomer coatings as liners on the inside of rail cars, and on surfaces such concrete, wood, etc. Such coatings should be highly conformal to the surface sprayed and should have excellent adhesion to the surface for the lifetime of the coating. Increasingly strict environmental regulations continue to reduce the volatile organic compound (VOC) emissions permitted during the application of such coatings. These requirements have forced the coatings to have higher solids and lower solvent contents and/or be entirely water-based systems.
The following excerpt from G. H. Brevoort, "Current Trends and Issues in Railcar Painting and Lining," Journal of Protective Coatings and Linings, December, 1991, is instructive.
"Without a doubt, the driving force in the past decade to develop high solids, improved protective coatings and linings with reduced VOCs has come from The Clean Air Act and its amendments. PA1 "Some residual benefits accrue from the use of high solids, VOC-conformant coatings and linings. For example, the number of gallons required is fewer, which results in fewer containers to ship, handle, open, apply and dispose of. While the price per gallon is higher, the contents per container are greater and go further so that fewer gallons are required. Much less sol-vent is being packaged, shipped and emitted. Often, the actual material cost for a job is reduced with more concentrated, high-solids products. Most important, many in the industry, includ-ing individual users, are being environmentally responsible. PA1 "It is not easy to formulate high solids, VOC-conformant coatings and linings. Solvents are not just removed and replaced with more solids. Among the problems encountered are maintaining suspension of the mixed products (non-settling), main-training their application and handling characteristics, producing coatings with the ability to build adequate drying and recoating times for practical use. Leveling of the applied coating film to create a smooth appearance has been particularly difficult to achieve."
One advantage of spray polyurea technology is that no foaming is noted even if the elastomer system is applied to a wet substrate. However, in some cases the moisture acts as a barrier to mechanical/chemical adhe-sion. There are commercially available water emulsifiable isocyanates used as substrate primers for spray elastomer systems. For wet substrates, these primers have poor penetration properties, giving poor elastomer coating system adhesion and possible foaming.
There is thus a continuing need to develop new systems to address the varied requirements of spray polyurea coatings. Various known poly-urea systems have been employed which address some of these parameters.
For example, U.S. Pat. No. 5,266,671 to Dudley J. Primeaux, II of Huntsman Petrochemical Corporation describes a spray polyurea elasto-mer which exhibits improved resistance to abrasion. The elastomer in-cludes an isocyanate, an amine terminated polyoxyalkylene polyol, a chain extender and a chemically sized filler material. The isocyanate is preferably a quasi-prepolymer of an isocyanate and a material selected from at least one polyol, a high molecular weight polyoxyalkyleneamine or a combination thereof. A method for making a spray polyurea elastomer which is substantially resistant to abrasion is also disclosed.
Spray polyurea elastomers made from an (A) component and a (B) component, where the (A) component has a quasi-prepolymer made from an isocyanate and an active hydrogen-containing material, such as a poly-oxyalkylenepolyamine, is described in U.S. Pat. No. 5,442,034 to Dudley J. Primeaux, II of Huntsman Petrochemical Corporation. The (B) component includes an amine resin, such as an amine-terminated polyoxyalkylene polyol which may be the same or different from the polyoxyalkylene poly-amine of the quasi-prepolymer. The viscosity of the (A) component is reduced by the inclusion of an organic, alkylene carbonate, such as ethyl-ene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate and the like. The alkylene carbonate also serves as a compatibilizer between the two components, thus giving an improved mix of the system.